Explicitly set allValues for hub variable

Currently, on latest grafana, the dashboards will currently
show 'no data' because the `$hub` variable is not set correctly
(see 2i2c-org/infrastructure#3237 for
details). The longer term solution to this is:

1. Move away from the deprecated graphPanel to timeseries objects
   for panel
2. #89

Both of these are being undertaken in
#90,
but in the meantime, this PR implements
[this
workaround](#90)
so end users can at least see data.

Author: yuvipanda

dashboards/jupyterhub.jsonnet

@@ -28,7 +28,10 @@ local templates = [
     // Allow viewing dashboard for multiple combined hubs
     includeAll=true,
     multi=true
-  ),
+  ) + {
+    // Explicitly set '$hub' to be `.*` when 'All' is selected, as we always use `$hub` as a regex
+    allValue: '.*',
+  },
 ];
 
 

dashboards/usage-report.jsonnet

@@ -18,7 +18,10 @@ local templates = [
     // Allow viewing dashboard for multiple combined hubs
     includeAll=true,
     multi=false
-  ),
+  ) + {
+    // Explicitly set '$hub' to be `.*` when 'All' is selected, as we always use `$hub` as a regex
+    allValue: '.*',
+  },
 ];
 
 local memoryUsageUserPods = barGaugePanel.new(

dashboards/user.jsonnet

@@ -26,7 +26,10 @@ local templates = [
     // Allow viewing dashboard for multiple combined hubs
     includeAll=true,
     multi=true
-  ),
+  ) + {
+    // Explicitly set '$hub' to be `.*` when 'All' is selected, as we always use `$hub` as a regex
+    allValue: '.*',
+  },
   template.new(
     'user_pod',
     datasource='$PROMETHEUS_DS',